The invention relates to a device and a method for measuring the mass and the moisture content of a material running through a spinning preparation machine. The invention also relates to a spinning preparation machine which is equipped with such a device. When “mass” is referred to here, this always means the mass per unit length.
In the spinning preparation process, first the raw material delivered in bale form is stripped off from the bale and, after cleaning and mixing, is fed to what is known as a card. There, the material is processed into fibre strands and is subsequently deposited in a cask-like container, what is known as a can. A plurality of such fibre strands are then combined and fed to a drawframe. Here, they are drawn with the aid of pairs of rollers, in order thereby to align the fibres in parallel and to obtain a correspondingly thinner strand which, in turn, is deposited in a can, in order then to be further processed later or elsewhere.
Throughout the entire spinning preparation process, it is advantageous to know the moisture content of the material, particularly during bale stripping. Process-accompanying moisture measurement has not been carried out hitherto. The check takes place in the form of random sampling and in a time-consuming way with the aid of gravimetric moisture measurement in the laboratory.
An essential parameter in the run through the drawframe is the drawing ratio. This can be changed by changing the speeds of successive pairs of rollers. The faster the following pair of rollers rotates in relation to a preceding pair, the more the material is drawn. If the fibre slivers have a relatively high mass on entry, the drawing ratio will be increased, in order to obtain an exit strand of always the same mass. The procedure is reversed when the fibre strands entering have a relatively low mass. It is therefore essential, at all events, to measure this mass before entry into the drawframe. Additional check measurements may also take place in these or downstream of these.
The check of the homogeneity of the fibre sliver mass is also necessary at the exit of the card. The control of the cards with a view to greater sliver homogeneity may be carried out with the aid of a process-accompanying measuring device for the sliver mass.
The measurement of the fibre sliver mass has hitherto being carried out by mechanical measuring means, for example by pairs of rollers which enclose the material strand between them and are pressed away from one another the more, the thicker this strand is. One problem, in this case, however, is the considerable speed at which these machines operate. Speeds of the material strands of up to 1000 m/min are typical here, this signifying speeds of approximately up to 17 m/sec. If changes in mass which extend over only a few centimetres of the strand are to be detected, therefore, the measuring means must have a time resolution of an order of magnitude of 1 msec or less. This can indeed be achieved somewhat satisfactorily by the mechanical means mentioned.
The disadvantage, however, is that an adverse influence is exerted on the material property by the mechanical frictional forces and by the material being pressed together. The thermal load leads to local heating or overheating, which can permanently damage the material.
The mechanical load leads to uneven distortions in the strand cross section. The structure, for example the degree of crimping, influences the measurement result (structural influence).
There is no process-accompanying measuring method for the moisture of the sliver material.